A resolver is a kind of a sensor for precisely measuring rotation speed and angle of a motor. Especially, a variable reluctance type resolver which includes the present invention has a relatively simple structure where both field winding and output winding are located at a stator and where a rotator having a shape of an ellipse or multiple poles is located within the stator.
Such a structure of the variable reluctance resolver has been introduced in Japanese Patent Application Publication H8-178610 “VARIABLE RELUCTANCE TYPE ANGLE DETECTOR” (Publication date: Jul. 12, 1996) and etc.
FIG. 1 is a drawing attached in the above Japanese Patent Application Publication. A rotor 10 is formed with four protrusion portions 10a, and a slot 11a of a stator 11 receives the field winding and the output winding. An alternating voltage induced by the rotator 10 is output while changing due to the protrusion portions 10a. 
FIG. 2 shows a rotator 20 of an improved shape. Eight elliptical protrusion portions 20a are formed on an outer peripheral surface with a predetermined interval of 45 degrees in the circular direction.
According to an experiment, if an exciting input voltage was 2.5 [Vrms] and 10 [kHz] with the rotator 20 having its shape as shown in FIG. 2, the corresponding output voltage 1, 2 was 2.96 [Vpkpk] (refer to FIG. 3).
However, the rotator 20 showing such a low output voltage and the resolver adopting the rotator have been required to have a structural improvement for an enhance in performance or in the same vein a cost cutting under the same condition of the output voltage.